1. Field of the Invention
The present invention concerns generally with scanning type image reading apparatuses using line sensor means wherein a plurality of photosensitive elements are arranged in line or the like arrangement, and more particularly with read-out data processing circuitry means adopted therein.
2. Description of the Prior Art
Conventional image reading apparatuses are arranged generally as shown in the block diagram of FIG. 1 of the accompanying drawings, by way of a preferred example. This example illustrates a conventional scanning type image reading apparatus. In this FIG. 1, numeral 100 represents a scan start signal generator which delivers a SOS-signal upon depression of a push button, not shown, on an operational panel also not shown.
The term "SOS" means "start of scan" as used throughout the present specification. In addition, the term "scan" means "scanning". Numeral 200 represents a scan motor drive circuit, while 300 represents the scan motor. Numeral 400 represents a CCD-line sensor comprising a number of CCD-sensors arranged in line, as an example, while 500 represents a CCD-driving circuit; 600 a clock pulse generator and 700 an original document.
With this arrangement, when the start button is depressed, a scan start signal "a" will be delivered from the generator 100 and fed to CCD-drive circuit 500, which acts thereupon, in synchronism with the operation of the scanning system, to deliver an instruction signal to CCD-line sensor 400. Based upon this instruction, CCD-line sensor 400 will then initiate read-out operation of original image on the document. The read-out timing is controlled and determined by use of clock pulses CP to be delivered from the generator 600 at predetermined constant cycles. In addition, the scan-start signal "a" is fed also to scan start drive circuit 200 for initiation of driving energization of scan motor 300. With energization of the latter, the scanning system is caused to move in the scanning direction which is perpendicular to the lengthwise direction of CCD-line sensor 400. In this way, the sensor 400 will execute the image read-out operation, covering the overall area of the original document image.
In this conventional image reading apparatus so far shown and described, the image-reading time period per one scanning line by the line sensor, or more specifically, moving time per scanning line, is controlled to a predetermined duration, as being fixed by clock pulses CP having constant duration periods. If there be certain mechanical troubles or errors in the scanning system, causing certain fluctuation in moving operation to occur therein by variation in the drive mode of the scan motor 300, the line pitch or more specifically the scanning length per line may naturally be subjected also to fluctuation. FIG. 2 represents schematically such variation in the line pitching as may be frequently and conventionally met with by uneven moving operation in the scanning system. In this drawing, X represents the lengthwise direction of the line sensor; Y represents the scanning direction. P1, P2, P3 . . . show successive line pitches.
When the line pitches are subjected to variation, disadvantageous distortion may take place in the read-out image, resulting in adverse effect in the image reproduceability which constitutes naturally a grave problem in the art.
This problem could be dissolved by improving the moving preciseness in the scanning system towards removal of moving fluctuations. In fact, however, it is impossibly difficult to remove such mechanical errors to a satisfying degree. In addition, adoption of such measures brings a tremendous increase of manufacturing cost.